Gasification of coal is an important part of China's coal chemical industry, especially in the increasingly tense conditions of oil resources. The detection and analysis of gas components is the premise of gasifier optimization control and an important parameter of other processes in the coal chemical industry. In addition, gas components are often tested in industrial fields such as blast furnaces, converters, coke ovens, and glass and ceramics. This article will introduce in detail a new multi-component infrared gas analysis method using electro modulation, together with the newly developed MEMS technology thermal conductivity TCD gas sensor and long-life electrochemical O2, H2S sensor developed integrated multi-component gas analyzer Gasboard -3100 technology applications. I hope to benefit you from testing gas components. 1. Infrared multi-component gas analysis The figure above shows the principle of NDIR infrared gas analysis: Taking CO2 analysis as an example, the infrared light source emits 1-20um of infrared light, which is absorbed by a gas chamber of a certain length and passes through a narrowband filter with a wavelength of 4.26μm. The sensor monitors the intensity of the infrared light transmitted through the 4.26 um wavelength to indicate the concentration of CO2 gas. If a detector with a quaternary element is placed at the detector end, four different wavelength filters, such as CO2 and CO, are used. , CH4, and reference filters allow the simultaneous measurement of CO2, CO, and CH4 in gas components in a single instrument. The gas analyzer Gasboard-3100 infrared measuring part technology has four different filters (CO2, CO, CH4, reference) installed on the integrated four-element detector, which can realize the simultaneous measurement of three gases (as shown below ). Filter integrated quad infrared detector 2. MEMS technology thermal conductivity TCD analysis At present, most domestic H2 analysis adopts thermal conductivity elements made of double platinum wire thermal elements, which has a large volume and low precision, and the sensor has a large dead space. The gas analyzer Gasboard-3100 adopts the latest internationally developed TCD gas sensor based on MEMS technology. It only needs to add an appropriate voltage to output a millivolt-level signal corresponding to the concentration. 3. Electrochemical Oxygen, Hydrogen Sulfide Analysis In gas composition analysis, O2 is a safety parameter, and sometimes H2S is also an important parameter. The gas analyzer Gasboard-3100 uses a long-lived (6 year) electrochemical O2 sensor and H2S sensor. This sensor is actually a miniature current generator, with a high precision preamplifier circuit, direct output and concentration The corresponding voltage enters the instrument measurement and control system. 4. Features of multi-component gas analyzer The gas analyzer Gasboard-3100 includes NDIR infrared gas detectors for CO, CO2, and CH4, measuring H2 TCD heat detectors, O2, H2S detectors; ADUC842 measurement and control systems and software; LCD, keyboards, printers, air pumps, And external devices such as alarms. Electric modulation infrared light source Conventional infrared gas analyzers use continuous infrared heat radiation type light sources, such as nickel crucible silk, silicon carbon rods and other infrared heating elements, which emit infrared light with wavelengths between 2 ~ 15μm, due to its large heat capacity, usually using a light cutting sheet Modulate the light source. Therefore, a synchronous motor is required to drive the rotation of the light-cutting sheet. The disadvantage is that there is a mechanical rotation. Poor vibration resistance, high offensive power, not suitable for portable devices. Secondly, in order to ensure the frequency of modulation, it is necessary to strictly synchronize the motor and the drive circuit, which makes the system complicated and the cost greatly increases. The gas analyzer Gasboard-3100 adopts a diamond-coated infrared light source newly developed in the world. The light source uses conductive amorphous carbon (CAC) multi-layer coating technology, heat capacity is very low, so the speed of heating and cooling is very fast, the maximum modulation frequency can reach 200Hz, the use of new electric modulation light source makes infrared gas analysis technology in the instrument volume, There are substantial improvements in costs, performance, etc. Gas interference correction In principle, due to the use of characteristic wavelengths between CO, CO2, and CH4, there is no mutual interference between measurements, but due to the limitations of the current filter production process, the filters have a certain bandwidth, CO and CO2, and There is some interference between CO2 and the reference channel, so there is certain interference between the components. If you do not calibrate, the measurement error will reach more than 10%, it is difficult to meet the requirements of industrial applications, such as after a single standard gas CO2 calibration If you enter the instrument with 70% CO without CO2, the CO2 reading will reach about 7%. In order to eliminate the mutual interference between the infrared analysis gases, the gas analyzer Gasboard-3100 is equipped with a 10-point calibration program, and the gas interference correction method is obtained by using a computer algorithm. Through the use of this method, the accuracy of CO, CO2, and CH4 can be achieved. More than 2%. Studies have shown that gas analysis systems that use single-component infrared gas analyzers in the past may result in inaccurate measurements if measurements are taken directly. At the same time, CO, CH4, N2, and O2 in the gas composition have little effect on the measurement accuracy of H2, mainly due to the influence of CO2. Through a lot of practice, it is proved that the effect of CO2 on H2 is linear. Every 1% CO2 will reduce the H2 content to 0.08%. If there is no CO2 calibration, when the CO2 content reaches 40%, the H2 error will exceed 3%. . This also fully shows that in order to obtain accurate gas composition analysis results, each component must be measured at the same time. Measuring flow control Although infrared and electrochemical gas analysis are less affected by the measured flow to a certain extent, for the TCD thermal conductivity H2 analysis, the stability of the gas flow is directly related to the measurement accuracy of H2. In order to ensure the stability of the measurement flow, the gas analyzer Gasboard-3100 uses a miniature plunger gas pump to compress the measurement gas to 0.2Mpa. After entering the gas analyzer through the gas pressure regulator and the flow regulator valve, the entire gas can be measured. The flow rate is maintained at 1L/min. The stability of the flow to a certain extent also improves the accuracy and stability of infrared and electrochemical gas measurements. Through the adoption of the above technologies, multi-component gas analyzers can achieve the following components and precision measurements (Table 1), and have been applied to industrial sites including blast furnaces, converters, gas generators, and have achieved good results. Table 1: Technical parameters of multi-component gas analyzer in conclusion (1) By adopting the new electric modulation infrared light source, the complicated and expensive motor modulation system of the conventional infrared gas analysis instrument is eliminated, and the system cost and power consumption are greatly reduced. Simultaneous measurement of CO, CO2, and CH4 is achieved. (2) Simultaneous on-line measurement of multiple components of gas is achieved by using TCD thermal conductivity of MEMS technology, and long-life O2, H2S electrochemical gas sensors and infrared gas measurement components. (3) There are certain mutual interferences between the infrared measurement components due to the limitation of the filter bandwidth, and the measurement accuracy of the components can be improved to more than 2% through the computer calibration algorithm. This also shows that the single component infrared Gas analyzers are used directly for gas analysis and are likely to cause inaccurate measurement data. (4) TCD thermal conductivity H2 analysis must be calibrated for CO2 gas, otherwise it may cause more than 3% error. Therefore, if only a single H2 analyzer is used without the calibration of other gas gases, the combined gas component monitoring system may not be able to obtain accurate measurement data. 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October 23, 2021